Modified arctic high pressure is centered over Ontario in south central Canada tonight. Low pressure has moved from Oklahoma last night to eastern Kentucky tonight. The high pushed a polar front in from the north across the Stateline today. The large difference in pressure between the low passing to our south today, and the hugh arctic high to the is called a pressure gradient, and with the strong pressure gradient, strong northeasterly winds pumped the cold air in from Canada across the Great Lakes, and over the Stateline. The low pressure storm system to our south just grazed northern Illinois with some light precipitation in the form of sprinkley rain showers overnight last night and early today. The cloud circulation around the low passing to our south was persistent for nearly the entire day. The sun made an appearance late in the day as the low edged off to the east, and very dry air came in from the north.
Here's how you can tell the air moving into the Stateline tonight is modified arctic air. Dew points over parts of central and southern Wisconsin were below zero early the evening. The only way dew points can be near, or below zero, when you have a widespread northerly air flow like today,is if the air came into our area from the arctic ice cap, and far northern reaches of Canada where temperatures are still below zero, and dew points are near 20 degrees below zero. That air is then advected southward with the southward moving high pressure area into the upper midwest. The temperatures naturally rise considerablly under the influence of the very strong late March sun. The dew point rises some too, but may still remain below zero despite the fact that afternoon temperatures under the sun modified air mass reach into the 30's and 40's. The air mass evolves into a very dry air mass with conditions like these with afternoon humidities less than 20% in many cases. It is desert like in it's humidity levels, but the source area was not from the desert... it was from the arctic. Interesting, eh?
Temperatures will drop to near 20 degrees tonight, as the cold air continues to pour across the area. In fact there may be some favored areas that may easily reach into the upper teens overnight. With the ridge sliding into the area tonight winds will diminish alot overnight under clear skies. Friday will be sunny and chilly as the ridge moves across the area. Winds will become southerly allowing for a brief warmup Friday night and Saturday as another low develops and spins itself up over the southern plains. The next storm system will take a track very similar to the last one across the southern tip of Illinois on late Saturday night into early Sunday bringing the Stateline another round of light rainfall. Right now it looks as if rainfall amounts will be in the 1/10 of an inch range with the heavier rains falling south of Interstate 80 once again. A new cold front and weak high pressure will follow in behind the departing low Sunday night into Monday, but the cold air following in behind this is of a much more moderate variety than what we are currently experiencing. That high will shift off to the east by late Monday into Tuesday, and a south to southwesterly surface wind flow will set up for much of the rest of next week. The Stateline will see temperatures climb each day through Thursday, likely reaching above 70 degrees by Thursday.
by Meteorologist
Eric Nefstead
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